Conveyor system

ABSTRACT

The conveyor system propels pallets by frictional contact between a rotating drive shaft and a drive wheel carried by the pallet. The drive wheel is pivotally mounted for movement between a drive position oblique to the drive shaft axis and a stop position with the wheel axis parallel to the drive shaft axis. Stops are selectively positioned to engage an arm connected to the drive wheel and move it to the stop position. The arm is provided with three vertical positions; a lower position where it passes the stop, an intermediate position where it engages the stop, and an upper position where it is released from the stop. Each pallet is provided with a rearwardly facing stop to engage the arm and prevent collision between the pallets.

United States Patent 1 Ribordy 1 Jan.7, 1975 1 CONVEYOR SYSTEM [75]Inventor: James E. Ribordy, South Beloit, Ill.

[73] Assignee: Rockford Automation Inc.,

Rockford, Ill.

[22] Filed: Nov. 7, 1973 [21] Appl. No.: 413,568

[52] U.S. Cl 104/166, 104/252, 198/19 [51] Int. Cl 1361b 13/00 [58]Field of Search 104/165, 166, 249, 252,

2/1964 Pravel 74/25 10/1972 Armstrong 104/249 X FOREIGN PATENTS ORAPPLICATIONS 1,025,997 France 74/25 Primary Examiner-Lloyd L. KingAssistant Examiner-Randolph A. Reese Attorney, Agent, or FirmMorsbach &Pillote [57] ABSTRACT The conveyor system propels pallets by frictionalcontact between a rotating drive shaft and a drive wheel carried by thepallet. The drive wheel is pivotally mounted for movement between adrive position oblique to the drive shaft axis and a stop position withthe wheel axis parallel to the drive shaft axis. Stops are selectivelypositioned to engage an arm connected to the drive wheel and move it tothe stop position. The arm is provided with three vertical positions; alower position where it passes the stop, an intermediate position whereit engages the stop, and an upper position where it is released from thestop. Each pallet is provided with a rearwardly facing stop to engagethe arm and prevent collision between the pallets.

20 Claims, 15 Drawing Figures PATENTED 7 SHEET 10F 8 IIINIII PATENTEDJAN 7 5 SHEET 3 OF 8 AA AZAL 7 PAIENTEDJAN 7 I975 SHEET 8 [IF 8PATENIEDJAH 7 i975 SHEET 7 UF 8 PATENTED JAN 7 I975 SHEET 8 BF 8CONVEYOR SYSTEM BACKGROUND The invention pertains to conveyor systemsand more particularly, to a conveyor system in which propulsion isachieved by traction between a drive wheel and a longitudinal rotaryshaft.

One early patent disclosing a rotary drive shaft and a pair oftravelling friction wheels engaged therewith at an angle to its axis,was issued May 7, 1889 to Whitcomb R. Judson, US. Pat. No. 402,674. Thismechanical movement has been adapted for street railways (see US. Pat.No. 423,872 issued Mar. 18, 1890 to said Judson); for air pressurecontrols (see U.S. Pat. No. 2,578,026 issued Dec. 11, 1951 to Daniel G.Taylor); for door openers (see US. Pat. No. 2,619,346 issued Nov. 25,1952 to Warren F. Weathers); and for conveyor systems (see US. Pat. No.3,356,040 issued Dec. 5, 1967 to Per Borje Fonden). In a conveyor systemit is frequently desirable to stop a pallet or support at a work stationand to quickly and easily accelerate it away from the work station.Sometimes it is desirable to allow selective pallets to pass a stop as,for example, when no work is to be performed on the workpiece carried bythe pallet.

SUMMARY position between the drive wheel and rotary shaft is selectivelycontrolled.

Still another object is to provide a conveyor system in accordance withthe foregoing object in which the position is controlled by an armoperatively connected to the drive wheel. Yet another object is toprovide a conveyor system in accordance with the above objects andincluding a stop for engaging the control arm to stop the pallet orsupport and in which the arm and stop may be moved relative to eachother to allow the pallet to again be driven.

A further object is to provide apparatus in accordance with theforegoing object in which the control arm is mounted for movementbetween a stop position and at least one other position spacedtherefrom.

A still further object is to provide a conveyor system in accordancewith the above objects in which a plurality of pallets or supports aredriven, and including apparatus to prevent collision between adjacentpallets.

A yet further object of the present invention is to pro vide a conveyorsystem in accordance with the foregoing object and including meansmounted on each pallet to engage the arm of a successive pallet invarious positions of the arm.

These, and other objects and advantages of the present invention, willbecome apparent as the same becomes better understood from the followingdetailed description when taken in conjunction with the accompaningdrawings.

DRAWINGS FIG. 1 is a front elevation of a machine incorporating thepresent invention;

FIG. 2 is a top plan view thereof;

FIG. 3 is a fragmentary top plan view of the right hand end of theapparatus shown in FIG. 2, and on an enlarged scale;

FIG. 4 is a cross-sectional view taken generally along line 4-4 of FIG.3; 8

FIG. 5 is a view taken generally along broken line 5-5 of FIG. 3 andwith portions broken away for a better illustration of the parts;

FIG. 6 is a fragmentary top plan view of the left hand end of theapparatus shown in FIG. 2, and on an enlarged scale;

FIG. 7 is a cross-sectional view taken generally along line 7-7 of FIG.6; 0

FIG. 8 is a top plan view of a pallet or support constructed inaccordance with the present invention;

FIG. 9 is a front elevation of the pallet shown in FIG.

FIG. 10 is a cross-sectional view taken generally along line 10-10 ofFIG. 8 and showing portions of the machine as well as positions of thecontrol arm in phantom lines;

FIG. 11 is a top view of the control arm as seen from line 11-11 in FIG.9;

FIG. 12 is a cross-sectional view taken along line 12-12 of FIG. 8, butshowing the rearwardly extending stop in elevation;

FIG. 13 is a top plan view of a work station constructed in accordancewith the present invention;

FIG. 14 is a longitudinal sectional view taken generally along line14-14 of FIG. 13; and

FIG. 15 is a cross-sectional view taken along line 15-15 of FIG. 14 andwith the cross-section through the pallet being taken along broken line15-15 of FIG. 8.

DESCRIPTION Reference is now made more particularly to the 'drawingswhich illustrate the best presently known mode of carrying out theinvention and wherein similar reference characters indicate the sameparts throughout the several views.

Referring to FIGS. 1 and 2, a machine indicated generally by the numeral20 has two longitudinal rotatable drive shafts 21 and 22 mountedparallel to each other. The drive shafts 21 and 22 are journaled in aplurality of spaced rollers such as shown at 19 in FIGS. 6 and 7. Therollers are located so the tops of the shafts are unobstructed for apurpose hereafter explained. A pair of spaced tracks 23 and 24 arearranged parallel to shaft 21 to define a pathway along which pallets Pmay move. At the left end of the machine, as seen in FIG. 2, is aturntable Tl associated with an inner arcuate track 27 whichinterconnects tracks 24 and 25; and an outer arcuate track 28 whichinterconnects tracks 23 and 26. Similarly, at the right end of themachine is a turntable T2 associated with an inner arcuate track 31interconnecting tracks 24 and 25; and an outer arcuate track 32interconnecting tracks 23 and 26. In this manner, the tracks form adefinite trackway or pathway in the form of a closed loop conveyor.

A motor M is arranged to drive gear boxes 41 and 42 connected to shafts21 and 22, respectively, by means of a transverse drive shaft 43. Athird gear box 44 is located intermediate the other two gear boxes torotate a third shaft 45 to drive the turntables T1 and T2. A pluralityof work stations, such as shown at A, B and C, are provided at spacedlocations along the tracks. One of the pallets P, carrying a workpiece,can be advanced to one of the work stations where the pallet is stoppedand an operation performed on the workpiece. By way of example, the workstation may have a unit such as disclosed in US. Pat. No. 3,609,839issued Oct. 5, 1971 to .l. T. Gonzales et al., and assigned to theassignee of the present invention. The unit disclosed in that patent maybe advantageously driven from shaft 45 if desired. After the operationis performed on the workpiece, the pallet is then conveyed to asucceeding station. The manner in which the pallet is stopped at thework station and conveyed away from the work station is hereafterdescribed in detail.

Referring now to FIGS. 8-12, the pallet or support P will be describedin detail. For reference, it should be understood that the front end ofthe pallet is shown at the right in FIGS. 8 and 9, while the rear end isat the left. Each pallet is provided with a plurality of wheels 51-54which engage the upper side of the trackway. Since the trackway shown inFIGS. 1 and 2 contains an arcuate portion, wheels 53 and 54 arepositioned nearer each other so that they can track around the smallerradius rails 27 and 31. Four other wheels 56-59 are mounted for rotationabout a vertical axis to engage the inner edge of the rails and preventside sway of the pallet as it is conveyed. Finally, four wheels 61-64are provided for engaging the bottom side of the tracks. In this manner,the pallets are conveniently permanently mounted in the trackways withthe utmost stability.

Each pallet P is provided with a freely rotatable driving wheel 67 whichis pressed against the top of the driving shaft 21 or 22. Wheel 67 isrotatably mounted in a yoke 68 (see FIG. 9) at the lower extremity of ashaft 69 (see FIG. Shaft 69 is rotatably mounted in bearings 71 and 72and the wheel 67 is pressed against the drive shaft by means of acompression spring 73, circumjacent shaft 69. A helical tension spring74 exerts a force on the yoke 68 to resiliently urge the axis ofrotation of the driving wheel 67 at an angle relative to the axis ofrotation of the drive shaft, the driving wheel and drive shaft being sooriented that the drive wheel in the angular position thereof contactsthe drive shaft along a horizontal tangent thereto. When the drive shaft21 or 22 is rotated, the wheel 67 will roll against the drive shaft.When the axis of the wheel 67 is disposed at an angle, for example 35,to the axis of the drive shaft, the rotation of the latter produces alongitudinal force on the drive wheel. This longitudinal force is thedriving force of the pallet and the drive wheel will follow a helicalpath along the drive shaft.

An outwardly extending arm 80 is connected to the yoke 68 and extendspast the side of the pallet as best seen in FIG. 8. The arm 80 is thusswingable with the drive wheel 67 and moves between a stop positionshown in solid lines in FIG. 8 and a drive position shown in phantomlines in FIG. 8 and disposed at an angle L which is the aforementioned35 degrees. Stops may be associated with the pallet assembly to limitthe movement between the two aforementioned positions. The arm 80advantageously carries a roller 81 at its outer extremity for a purposewhich will hereafter become apparent.

Referring now to FIGS. 10 and 15, it can be seen that the arm can assumethree different vertical positions, 80A, 80B, 80C, the latter two ofwhich are shown in phantom lines in those FIGS. A stop, as indicated at85 in FIG. 15 may be provided at each station. In the intermediatevertical position 808, the arm 80 is initially at the drive position andthe roller 81 will engage the stop 85 as shown at 818 in FIG. 15, andswing the arm 80 and wheel 67 to the aforementioned stop position. Whenlifted to the uppermost position 80C, it can be seen that the arm 80will pass over the stop 85. Torsion spring 74 will then urge the arm 80to the aforedescribed drive position and the pallet will then be drivenaway from the stop. The lowermost position 80A may be considered aby-pass position since the arm will pro ceed past the stop 85 in thisposition. Preferably, the stop 85 is shaped for this purpose. As shown,the stop 85 is generally C-shaped, having a roller engaging leg 86 and arecessed portion 87. The upper edge 88 is inclined downwardly at anangle about tangent to drive shaft 22 to allow clearance for arm 80 whenin the uppermost position 80C. A detent (not shown) may be provided tohold the arm 80 in the lower position 80A. The lower position is aparticularly advantageous position since the pallet P will then bypassall work stations. This may be utilized, by way of example, when theworkpiece carried by the pallet has been rejected and no furtheroperations are to be performed thereon. In this manner, any pallet withits arm in the bypass position 80A is ignored by the work stations andcauses no delay in the operation thereof.

Referring again to FIGS. 8, 9 and 12, it can be seen that each pallethas a rearwardly extending stop 89 which engages the arm 80 of asucceeding pallet P. It should be understood that the arm 80 preferablyengages the stop 89 in all of its above-mentioned vertical positions;however, it is absolutely necessary that it engages the stop 89 in thetwo lower positions 80A, 80B to stop a succeeding pallet from runninginto the preceding pallet. This is advantageous when the precedingpallet has been stopped at a work station. This combination also allowsthe pallets to be moved independently of each other without any othercontrols along the conveyor system.

A stop arrangement, generally designated 90, is provided at the entranceof each turntable T1 and T2 to stop the incoming pallet P if there isanother pallet at the outlet of the turntable. As best shown in FIG. 4,the stop arrangement 90 includes an upright shaft 92 slidably mountedthrough a support 93 and resiliently urged by a compression spring 94 toa raised position. At the lower end of shaft 92 are stop fingers 90a and90b for engaging the roller 81 when the arm is in positions 80A and 80B,respectively. An actuating finger 96 is provided intermediate the endsof shaft 92 and is associated with an actuating arm 101 which ispivotally mounted intermediate its ends. A plurality of ramps 102 aremounted around the periphery of the tumtables T1 and T2. The ramps arearranged to engage a roller 101a and cause the actuating arm 101 to bemoved to an actuating position to depress the shaft 92. In this manner,the stops 90a and 90b are moved to a release position allowing a palletto be advanced into the turntable. A plurality of L-shaped fingers 104are arranged around the periphery of the turntable and may engage aroller or detent (not shown) on the pallet P and feed it from driveshaft 22 to drive shaft 21 in the case of turntable T1 and vice versafor turntable T2. Other mechanism may be used for the turntable ifdesired, for example, a belt conveyor, a chain conveyor, or the like.

As indicated previously, actuating arm 101 is movable between anactuating position to engage finger 96 an an inoperative position whichis illustrated in FIGS. 3 and 6. For this purpose, actuating arm 101 isswingably mounted on a yoke 105 which is pivotally mounted by an uprightshaft 106. The entire mechanism is urged to the actuating position byspring 108, and is moved to the inoperative position by means of leverarms 111 and 112 in response to a pallet P at the outlet of theturntable. Such a pallet may be sensed by an electric eye or otherarrangement and, in the embodiment shown, its position is mechanicallysensed. As shown, a sensing arm 114 carrying a plurality of rollers 115is rigidly secured to arm 112. The rollers 115 are positioned forengagement by the side of pallet stop 89 as can be seen in FIGS. 3 and6. The engagement by the pallet stop 89 deflects arm 114 inwardlythereby transmitting motion through arms 112 and 111 to pivot theactuating arm 101 to an inoperative position.

In addition to starting or stopping the movement of the pallet P, it isalso possible to control its movement at a lesser speed than maximum.This may be accomplished by controlling the angle of inclination betweenthe axis of the drive wheel 67 and the axis of the drive shaft 21 or 22.For this purpose, a cam surface 117 may be provided generally parallelto one of the drive shafts, as shown in FIGS. 2 and 3. The cam surfacepreferably has a tapered inlet 118 to engage the roller 81 and anothersurface spaced from the drive shaft 22 a distance so that the roller 81will keep the arm 80 at the desired angle to the drive shaft. By sodoing, the speed of the pallet can be selectively reduced through agiven zone. This is advantageous, for example, should one wish to have adrying operation incorporated in the conveyor system. Speed slowdownsare also useful for inspection purposes, loading stations and the like.After passing the cam surface 117, the spring 74 would again urge thewheel 67 to the maximum angle with regard to the drive shaft.

It is deemed evident from the above description that the pallet P maymove freely and easily along the rails. At the work stations, forexample work station A, it is desirable that the pallet P be securelyheld in position during the time it is stopped. For this purpose, frontand rear locating or positioning pins 120 and 122, respectively (seeFIGS. 13-14), are mounted in an upright position to move upwardly intocorresponding openings 120a and 122a (see FIG. 8) in the pallet P. Inthe embodiment illustrated, each opening is defined by a sleeve having aforce fit in a larger opening in the pallet. Both locating pins 120 and122 are tapered at their tops to overcome slight misalignment with theopenings 120a and 122a when the locating pins are raised upwardly. Therear locating pin 122 is round in cross section to align the pallet bothlaterally and longitudinally. The top portion of the front locating pin120 is relieved as at 121 on each of the longitudinal sides, as shown inFIG. 14, so that it serves to engage the corresponding opening 120 onlyat the lateral sides thereof, as shown in FIG. 15. In this manner, veryslight differences in the positions of the openings 120a and 122a can beaccommodated.

As explained above, the locating pins 120 and 122 are mounted in anupright position for movement in a vertical direction. As shown in FIG.15, the locating pin 120 is movable between a lower or release positionshown in phantom lines and a raised or inserted position shown in fulllines. The stroke S of the locating pin 120 is indicated in that FIG.Locating pin 120 is slidably mounted by means of a sleeve 124 which isheld in position by brackets 125 and 126. The lower end of the locatingpin 120 is connected to the rod 132 of a pneumatic actuator 134 by meansof a coupling 136. Locating pin 122 is similarly mounted, and theidentical structure to that described above is indicated by the samenumerals with the postscript prime and further description is deemedunnecessary.

When the pallet P approaches the work station A, the arm will engage thestop when the arm is in its intermediate position 808. This will causethe pallet to be stopped in the manner previously described. Anoutwardly extending L-shapcd finger 141 secured adjacent the front ofthe pallet P simultaneously engages the lever arm 142 of a switch 143(see FIG. 15). Switch 143 controls the supply of fluid under pressure tothe actuators 134 and 134. Switch 143 may be in the supply line or itmay be arranged to control another switch in the supply line. Thiscauses the actuators to move to their extended or raised position shownin FIGS. 14 and 15 and extend the locating pins and 122. After apreselected time lapse, another switch (not shown) may be actuated tocause the actuators 134 and 134' to retract the locating pins. The timelapse can be selected dependent upon the duration of the operation atthe work station.

After the work has been completed at the work station and the locatingpins retracted, a kick-off rod 146 is extended from its lower positionshown in FIG. 15 to the extended position shown in phantom lines in thatFIG. The kick-off rod engages the bottom side of the arm 80 and raisesit to the upper position 80C where it passes over the stop 85. Thespring 74 urges the wheel 67 to the previously described angle with thedrive shaft and the pallet P is driven from the work station.

A particularly advantageous arrangement is provided to coordinateretraction of the locating pin 120 with the raising of the kick-off rod146. For this purpose, a lever 148 is pivotally mounted intermediate itsends on a pivot shaft 149. One end of lever 148 is disposed adjacent thelower portion of locating pin 120 while the other end is operativelyconnected to kick-off rod 146 by means of a pin 150. At the one end oflever 148 is a detent 152 which is spring urged to the position shown infull lines. At this position, the detent is engaged by a collar 154mounted on the lower end of locating pin 120. As the locating pin 120 isretracted, collar 154 engages detent 152 and swings the lever arm toraise the kick-off rod 146. When the lever arm 148 and kick-off rod 146are in the raised position, the collar 154 passes by the detent 152 andthe kick-off rod 146 is returned to its lower position by means ofcompression spring 156. Because of the mounting of the detent 152, itcan be seen that it will swing out of position when the locating rod 120is raised and collar 154 passes by it. Its spring will then urge thedetent to the position shown in solid lines to again be engaged by thecollar 154 when the locating rod 120 is again retracted. In this manner,the kick-off arm is extended when the locating pin 120 is retracted.

While a preferred embodiment of the invention has herein beenillustrated and described, this has been done by way of illustration andnot limitation, and the invention should not be limited except asrequired by the scope of the appended claims.

What is claimed is:

1. In a conveyor system including pallets mounted for movement along adefinite pathway by frictional contact between a rotating drive shaftarranged parallel to the pathway and at least one drive wheel carried bythe pallet, the drive wheel being pivotally mounted on the pallet formovement between a drive position oblique to the longitudinal axis ofthe drive shaft and a stop position parallel to said axis, and means forresiliently urging the drive wheel toward the drive position; theimprovement comprising; an arm extending laterally of said pathway andoperatively connected to the drive wheel for moving the drive wheel fromthe drive position to the stop position; means mounting at least aportion of the arm for vertical movement between a first normal positionand at least one other position vertically spaced therefrom; a stopmounted adjacent the pathway for engagement by the arm when in its firstposition to stop the pallet; and the stop being shaped so that it is notengaged by the arm when the arm is in said other position.

2. A conveyor system as set forth in claim 1 including a pallet mountedstop for engaging the arm of a successive pallet in all positions of thearm to stop the successive pallet when the preceding pallet is stopped.

3. A conveyor system as set forth in claim 2 in which the drive positionis at an angle of approximately 35 from the stop position; and in whichthe means for resiliently urging the drive wheel toward the driveposition is a spring which is operative in all positions of the arm.

4. A conveyor system as set forth in claim 2 including a roller at theouter end of the arm for engaging said stop.

5. A conveyor system as set forth in claim 4 including a cam facemounted adjacent the drive shaft to engage the roller when the arm is innormal position and deflect the arm and hence the drive wheel to aposition intermediate its drive position and its stop position, wherebythe movement of the pallets is retarded but not stopped.

6. A conveyor system as set forth in claim 1 in which the means mountingat least a portion of the arm for vertical movement provides a thirdposition vertically spaced from said other two positions; and the stopbeing shaped so that it is not engaged by the arm when in said thirdposition.

7. A conveyor system as set forth in claim 6 including means for holdingthe arm in said third position so that the pallet passes the stop.

8. A conveyor system as set forth in claim 7 wherein the normal positionis intermediate the other two positions, and the third position is belowthe normal position.

9. A conveyor system as set forth in claim 7 including a pallet mountedstop for engaging the arm of a successive pallet in at least the normaland third positions of the arm to stop the successive pallet when thepreceding pallet is stopped.

10. A conveyor system as set forth in claim 1 in which the pathway isdefined by two parallel tracks; each track having an upper surface andan inner surface facing the opposite track; and the pallet having aplurality of wheels rotatably mounted thereon for engaging the upper andinner surfaces of the tracks.

11. A conveyor system as set forth in claim 10 including a secondrotating shaft laterally spaced from the other shaft and a second pairof parallel tracks parallel to the second shaft; two arcuate tracksinterconnecting the pairs of parallel tracks to further define saidpathway; and means associated with the arcuate tracks for conveying thepallets from the first pair of tracks, across the arcuate tracks, to thesecond pair of tracks.

12. In a conveyor system including: a frame, a drive shaft rotatablymounted on the frame, means for rotating the drive shaft, a plurality ofsupports mounted for movement parallel to the drive shaft, each supporthaving a drive wheel frictionally engaged with the drive shaft, and thedrive wheel being pivotally mounted for movement between a driveposition oblique to the axis of the drive shaft and a stop position inwhich the wheel axis is parallel to the drive shaft axis, theimprovement comprising: an arm extending laterally of the drive shaftand operatively connected to the drive wheel for moving the drive wheelfrom the drive position to the stop position; stop means supported onthe frame spaced from the drive shaft and located for engagement by thearm to stop the pallet; means for effecting relative movement betweenthe arm and stop means to dis engage the arm; means for returning thedrive wheel to the drive position upon such disengagement; and meansmounting at least a portion of the arm for vertical movement between afirst normal position where it can engage the stop and another positionwhere it does not engage the stop.

13. The combination of claim 12 including means for releasably holdingthe arm in said other position.

14. The combination of claim 13 in which said other position is belowthe normal position, the means mounting at least a portion of the armfor vertical movement provides a release position vertically spacedabove the normal position, and the stop being shaped so that it isengaged only when the arm is in said normal position.

15. The combination of claim 14 including a second rotating drive shaftlaterally spaced from and generally parallel to said drive shaft; thedrive shafts each having ends; and means at the ends of the drive shaftsfor conveying the supports from the end of one drive shaft to a positionin which the drive wheel of the support is engaged with the other driveshaft; thereby providing a closed loop conveyor system.

16. The combination of claim 12 including means on each support forengaging the arm of a successive support in various positions thereof tostop the successive support when the preceding support is stopped.

17. A conveyor system comprising, in combination, a frame; first andsecond drive shafts rotatably mounted on the frame in spaced relation toeach other; means for rotating the drive shafts; a first pair of tracksmounted parallel to the first drive shaft; a second pair of tracksmounted parallel to the second drive shaft; a pair of arcuate tracksinterconnecting the first and second pairs of tracks; a plurality ofvehicles movably supported on the tracks; a drive wheel on each vehicle;means mounting the drive wheel for engagement with the drive shafts andat a position oblique to the axis of the drive shafts to drive thevehicle as the drive shafts are rotated; a transfer mechanism associatedwith the arcuate tracks for transferring the vehicle from the first pairof tracks to the second pair of tracks; and means associated with thetransfer mechanism for rendering it inoperative when there isinsufficient room on the second pair of tracks for another vehicle.

18. A closed loop conveyor system comprising: a frame; a first driveshaft rotatably mounted on the frame; a second drive shaft rotatablymounted on the frame laterally spaced from and generally parallel to thefirst drive shaft; means for rotating the drive shafts; a first pair oftracks mounted parallel to the first drive shaft; a second pair oftracks mounted parallel to the second drive shaft; said first and secondpairs of tracks each having ends; a pair of arcuate tracks at the endsof and interconnecting the first and second pairs of tracks; therebyproviding a closed loop; a plurality of vehicles movably supported onthe tracks; a drive wheel on each vehicle; means mounting each drivewheel for engagement with the drive shafts and at a drive positionoblique to the axis of the drive shafts to drive the vehicle as thedrive shafts are rotated; a transfer mechanism associated with each pairof arcuate tracks for transferring the vehicle from the first pair oftracks to the second pair of tracks; and means associdriven by the driveshaft; an arm operatively connected I to each drive wheel and extendingoutwardly therefrom for moving the drive wheel from the drive positionto the stop position when the arm is contacted; and a vehicle-mountedstop for contacting the arm of a successive vehicle to stop the vehiclewhen the preceding vehicle is stopped.

20. The combination of claim 18 in which each drive wheel is mounted formovement between the drive position and a stop position in which thewheel is not driven by the drive shaft; an arm extending laterally ofthe drive shaft toward the inside of the said closed loop, andoperatively connected to the drive wheel for moving the drive wheel fromthe drive position to the stop position; stop means supported on theframe at the inside of said closed loop and located for engagement bythe arm to stop the vehicle; and means for effecting relative movementbetween the arm and the stop means to disengage the arm.

l l =l

1. In a conveyor system including pallets mounted for movement along adefinite pathway by frictional contact between a rotating drive shaftarranged parallel to the pathway and at least one drive wheel carried bythe pallet, the drive wheel being pivotally mounted on the pallet formovement between a drive position oblique to the longitudinal axis ofthe drive shaft and a stop position parallel to said axis, and means forresiliently urging the drive wheel toward the drive position; theimprovement comprising; an arm extending laterally of said pathway andoperatively connected to the drive wheel for moving the drive wheel fromthe drive position to the stop position; means mounting at least aportion of the arm for vertical movement between a first normal positionand at least one other position vertically spaced therefrom; a stopmounted adjacent the pathway for engagement by the arm when in its firstposition to stop the pallet; and the stop being shaped so that it is notengaged by the arm when the arm is in said other position.
 2. A conveyorsystem as set forth in claim 1 including a pallet mounted stop forengaging the arm of a successive pallet in all positions of the arm tostop the successive pallet when the preceding pallet is stopped.
 3. Aconveyor system as set forth in claim 2 in which the drive position isat an angle of approximately 35* from the stop position; and in whichthe means for resiliently urging the drive wheel toward the driveposition is a spring which is operative in all positions of the arm. 4.A conveyor system as set forth in claim 2 including a roller at theouter end of the arm for engaging said stop.
 5. A conveyor system as setforth in claim 4 including a cam face mounted adjacent the drive shaftto engage the roller when the arm is in normal position and deflect thearm and hence the drive wheel to a position intermediate its driveposition and its stop position, whereby the movement of the pallets isretarded but not stopped.
 6. A conveyor system as set forth in claim 1in which the means mounting at least a portion of the arm for verticalmovement provides a third position vertically spaced from said other twopositions; and the stop being shaped so that it is not engaged by thearm when in said third position.
 7. A conveyor system as set forth inclaim 6 including means for holding the arm in said third position sothat the pallet passes the stop.
 8. A conveyor system as set forth inclaim 7 wherein the normal position is intermediate the other twopositions, and the third position is below the normal position.
 9. Aconveyor system as set forth in claim 7 including a pallet mounted stopfor engaging the arm of a successive pallet in at least the normal andthird positions of the arm to stop the successive pallet when thepreceding pallet is stopped.
 10. A conveyor system as set forth in claim1 in which the pathway is defined by two parallel tracks; each trackhaving an upper surface and an inner surface facing the opposite track;and the pallet having a plurality of wheels rotatably mounted thereonfor engaging the upper and inner surfaces of the tracks.
 11. A conveyorsystem as set forth in claim 10 including a second rotating shaftlaterally spaced from the other shaft and a second pair of paralleltracks parallel to the second shaft; two arcuate tracks interconnectingthe pairs of parallel tracks to further define said pathway; and meansassociated with the arcuate tracks for conveying the pallets from thefirst pair of tracks, across the arcuate tracks, to the second pair oftracks.
 12. In a conveyor system including: a frame, a drive shaftrotatably mounted on the frame, means for rotating the drive shaft, aplurality of supports mounted for movement parallel to the drive shaft,each support having a drive wheel frictionally engaged with the driveshaft, and the drive wheel being pivotally mounted for movement betweena drive position oblique to the axis of the drive shaft and a stopposition in which the wheel axis is parallel to the drive shaft axis,the improvement comprising: an arm extending laterally of the driveshaft and operatively connected to the drive wheel for moving the drivewheel from the drive position to the stop position; stop means supportedon the frame spaced from the drive shaft and located for engagement bythe arm to stop the pallet; means for effecting relative movementbetween the arm and stop means to disengage the arm; means for returningthe drive wheel to the drive position upon such disengagement; and meansmounting at least a portion of the arm for vertical movement between afirst normal position where it can engage the stop and another positionwhere it does not engage the stop.
 13. The combination of claim 12including means for releasably holding the arm in said other position.14. The combination of claim 13 in which said other position is belowthe normal position, the means mounting at least a portion of the armfor vertical movement provides a release position vertically spacedabove the normal position, and the stop being shaped so that it isengaged only when the arm is in said normal position.
 15. Thecombination of claim 14 including a second rotating drive shaftlaterally spaced from and generally parallel to said drive shaft; thedrive shafts each having ends; and means at the ends of the drive shaftsfor conveying the supports from the end of one drive shaft to a positionin which the drive wheel of the support is engaged with the other driveshaft; thereby providing a closed loop conveyor system.
 16. Thecombination of claim 12 including means on each support for engaging thearm of a successive support in various positions thereof to stop thesuccessive support when the preceding support is stopped.
 17. A conveyorsysTem comprising, in combination, a frame; first and second driveshafts rotatably mounted on the frame in spaced relation to each other;means for rotating the drive shafts; a first pair of tracks mountedparallel to the first drive shaft; a second pair of tracks mountedparallel to the second drive shaft; a pair of arcuate tracksinterconnecting the first and second pairs of tracks; a plurality ofvehicles movably supported on the tracks; a drive wheel on each vehicle;means mounting the drive wheel for engagement with the drive shafts andat a position oblique to the axis of the drive shafts to drive thevehicle as the drive shafts are rotated; a transfer mechanism associatedwith the arcuate tracks for transferring the vehicle from the first pairof tracks to the second pair of tracks; and means associated with thetransfer mechanism for rendering it inoperative when there isinsufficient room on the second pair of tracks for another vehicle. 18.A closed loop conveyor system comprising: a frame; a first drive shaftrotatably mounted on the frame; a second drive shaft rotatably mountedon the frame laterally spaced from and generally parallel to the firstdrive shaft; means for rotating the drive shafts; a first pair of tracksmounted parallel to the first drive shaft; a second pair of tracksmounted parallel to the second drive shaft; said first and second pairsof tracks each having ends; a pair of arcuate tracks at the ends of andinterconnecting the first and second pairs of tracks; thereby providinga closed loop; a plurality of vehicles movably supported on the tracks;a drive wheel on each vehicle; means mounting each drive wheel forengagement with the drive shafts and at a drive position oblique to theaxis of the drive shafts to drive the vehicle as the drive shafts arerotated; a transfer mechanism associated with each pair of arcuatetracks for transferring the vehicle from the first pair of tracks to thesecond pair of tracks; and means associated with the transfer mechanismfor rendering it inoperative when there is insufficient room for anothervehicle.
 19. The combination of claim 18 in which each drive wheel ismounted for movement between the drive position and a stop position inwhich the wheel is not driven by the drive shaft; an arm operativelyconnected to each drive wheel and extending outwardly therefrom formoving the drive wheel from the drive position to the stop position whenthe arm is contacted; and a vehicle-mounted stop for contacting the armof a successive vehicle to stop the vehicle when the preceding vehicleis stopped.
 20. The combination of claim 18 in which each drive wheel ismounted for movement between the drive position and a stop position inwhich the wheel is not driven by the drive shaft; an arm extendinglaterally of the drive shaft toward the inside of the said closed loop,and operatively connected to the drive wheel for moving the drive wheelfrom the drive position to the stop position; stop means supported onthe frame at the inside of said closed loop and located for engagementby the arm to stop the vehicle; and means for effecting relativemovement between the arm and the stop means to disengage the arm.